1. Field of the Invention
The present invention relates to a hologram recording apparatus and a hologram recording method that perform recording by holography.
2. Description of the Related Art
Development of hologram recording apparatuses that record data by holography has advanced.
In hologram recording apparatuses, a modulated (data-superimposed) signal beam and an unmodulated reference beam are produced from laser light, and are applied onto the same point on a hologram recording medium. As a result, the signal beam and the reference beam interfere with each other on the hologram recording medium, and a diffraction grating (hologram) is formed at the point where the beams are applied; that is, data is recorded on the hologram recording medium.
By applying a reference beam onto a medium on which a hologram is recorded, diffracted light (reproduction light) is produced from the recorded diffraction grating. Since the reproduction light includes the same data superimposed on the signal beam during recording, it is received by a photoreceptor to reproduce recorded signals.
Multiple holograms are sometimes formed on a hologram recording medium in order to record much information. In this case, holograms can be formed not only at different positions on the hologram recording medium, but also on the same position (or in overlapping regions). This recording method is so-called multiplex recording. Various multiplex recording methods, such as angle multiplexing, wavelength multiplexing, and rotation multiplexing, have been proposed hitherto.
For example, in angle multiplexing, holograms are formed on the same position on a hologram recording medium while changing the incident angle of a reference beam. By using a reference beam similar to the reference beam used for recording during reproduction, reproduction light and data corresponding to a plurality of holograms formed on the same position can be obtained.
Hologram recording apparatuses have been developed which increase the recording capacity by utilizing phase correlation multiplexing as a kind of multiplexing method, as disclosed in Japanese Unexamined Patent Application Publication No. 11-242424.